#/usr/bin/env python
# -*- coding: utf-8 -*-
## http://www.freebuf.com/articles/network/41127.html
import socket
import struct

class IP(object):
    def __init__(self, source, destination):
        self.version = 4
        self.ihl = 5
        self.tos = 0
        self.tl = 0
        self.id = 54321
        self.flags = 0
        self.offset = 0
        self.ttl = 255
        self.protocol = socket.IPPROTO_TCP
        self.checksum = 0
        self.source = socket.inet_aton(source)
        self.destination = socket.inet_aton(destination)

    def pack(self):
        ver_ihl = (self.version << 4) + self.ihl
        flags_offset = (self.flags << 13) + self.offset
        ip_header = struct.pack("!BBHHHBBH4s4s",
                                ver_ihl,
                                self.tos,
                                self.tl,
                                self.id,
                                flags_offset,
                                self.ttl,
                                self.protocol,
                                self.checksum,
                                self.source,
                                self.destination)

ipobj = IP("127.0.0.1", "127.0.0.2")
ipobj.source = "localhost"


class TCP(object):
    def __init__(self, srcp, dstp):
        self.srcp = srcp
        self.dstp = dstp
        self.seqn = 0
        self.ackn = 0
        self.offset = 5
        self.reserved = 0
        self.urg = 0
        self.ack = 0
        self.psh = 0
        self.rst = 0
        self.syn = 0
        self.fin = 0
        self.window = socket.htons(5840)
        self.checksum = 0
        self.urgp = 0
        self.payload = ""
    def pack(self, source, destination):
        data_offset = (self.offset << 4) + 0
        flags = self.fin + (self.syn << 1) + (self.rst << 2) + (self.psh << 3) + (self.ack << 4) + (self.urg << 5)
        tcp_header = struct.pack("!HHLLBBHHH",
                                 self.srcp,
                                 self.dstp,
                                 self.seqn,
                                 self.ackn,
                                 data_offset,
                                 flags,
                                 self.window,
                                 self.checksum,
                                 self.urgp)
        # pseudo header fields
        source_ip = source
        destination_ip = destination
        reserved = 0
        protocol = socket.IPPROTO_TCP
        total_length = len(tcp_header) + len(self.payload)
        # Pseudo header
        psh = struct.pack("!4s4sBBH",
                          source_ip,
                          destination_ip,
                          reserved,
                          protocol,
                          total_length)
        psh = psh + tcp_header + self.payload
        tcp_header = struct.pack("!HHLBBH",
                                 self.srcp,
                                 self.dstp,
                                 self.seqn,
                                 self.ackn,
                                 data_offset,
                                 flags,
                                 self.window)
        tcp_header = struct.pack("H", tcp_checksum) +\
                     struct.pack("H", self.urgp)
        
